1). Field of the Invention
This invention relates to visual display systems of the kind which are mounted to the head of a viewer.
2). Discussion of Related Art
Miniature display devices may be used in a number of ways, although they are particularly well suited for use in head-mounted displays. Head-mounted displays which are mounted on the head of a viewer have typically been bulky and large. These displays often use small cathode ray tubes to project an image toward a viewer's eye. Numerous head-mounted displays are known in the art. See, for example, the book Head-Mounted Displays, by James E. Melver, and Kirk Moffitt which is published by McGraw Hill. These displays are sometimes also referred to as displays which are brought to the head of a viewer.
Certain head-mounted displays use a liquid crystal technology to provide a visual display rather than cathode ray tubes. For example, U.S. Pat. No. 5,596,451 describes a miniature image generator which uses a liquid crystal display device in conjunction with magnifying mirrors to generate an image which may be used with a head-mounted display. Examples of liquid crystal display devices which may be used in this context may be found in U.S. Pat. Nos. 5,566,010 and 5,426,526.
While liquid crystal display devices in head-mounted displays provide certain advantages in terms of weight and bulk, these displays are often poorly suited for displaying high quality images because of short optical paths required by a small enclosure which houses the head-mounted display. For example, these displays, for purposes for miniaturization, usually include low f-number lenses. Low f-number lenses cause aberrations of light which travels through outer regions of such lenses. One such aberration is loss of image brightness.